1. Field of the Invention
The present invention relates to a Micro Electro Mechanical System (MEMS) device and a fabrication method thereof. More particularly, the present invention relates to an electrostatic driving MEMS device having a driving electrode in an embedded structure and a fabrication method thereof.
2. Description of the Related Art
Micro Electro Mechanical System is a technology that implements mechanical and electrical parts, using semiconductor processing techniques. A conventional MEMS device generally includes floating driving parts that are movable over a substrate in order for the device fabricated using MEMS technology to perform mechanical operations.
FIG. 1 illustrates a cross-sectional view schematically showing a conventional MEMS device. The conventional MEMS device of FIG. 1 includes a substrate 10, a fixing part 30 attached to the substrate 10, and a driving part 40 extending from the fixing part 30. The fixing part 30 is generally referred to as an anchor or a support. The fixing part 30 connects the driving part 40 to the substrate 10.
The driving part 40 is spaced to float over the substrate 10. The driving part 40 is movable in an upward and downward direction, as shown by the broken lines in FIG. 1. The movement of the driving part 40 is controlled by a predetermined driving force from an electrode part 20 formed on the substrate 10. The driving part 40 is typically fabricated in a shape such as a beam, a membrane, or the like depending on device requirements.
FIG. 2A to FIG. 2E illustrate views for sequentially illustrating stages in a process for fabricating a conventional electrostatic drive-type RF MEMS device.
As shown in FIG. 2A, a driving electrode layer 220, for providing an electrostatic driving force, is formed on a substrate 210 through patterning. In FIG. 2B, a metal layer is formed on the substrate and then the metal layer is patterned so metal layer areas 230 having similar shapes remain. The metal layer areas 230 are an anchor part to acts as a fixing part fixed on the substrate 210 and an RF line to act as input and/or output terminals of an RF signal. The metal layer areas 230 are formed in a thick layer having a thickness of 2 to 3 xcexcm in consideration of the skin depth effect.
Next, referring to FIG. 2C, an insulation layer 240 is formed to surround the driving electrode layer 220 formed on the substrate 210.
Thereafter, as shown in FIG. 2D, a sacrificial layer 250 is formed on the resultant structure on the substrate 210. The sacrificial layer 250 over the anchor part fixed on the substrate 210 is etched through predetermined patterning. Referring to FIG. 2E, a MEMS structure layer is then formed on the patterned sacrificial layer 250. The MEMS structure layer includes a driving part 260 and a connection part 261.
Subsequently, predetermined etching access holes (not shown) are formed in the driving part 260 of the MEMS structure layer, and an etchant is supplied through the etching access holes to selectively etch only the sacrificial layer 250. Accordingly, as shown in FIG. 2E, a conventional MEMS device is fabricated such that the driving part 260 floats over the substrate 210 after the removal of the sacrificial layer 250.
As stated above, a conventional fabrication process proceeds regardless of a step-height difference between the metal layer areas 230 and the driving electrode layer 220. Consequently, a step-height difference between the metal layer areas 230 and the driving electrode layer 220 causes the driving part 260, which is formed by a subsequent procedure, to be formed unevenly, as may be seen in FIG. 2E. Thus, the reliability of such a MEMS device decreases. Moreover, since unevenness of the driving part is not expected during the designing of the device, a significant error exists between the design of the device and the fabrication process. Further, unevenness in the driving part 260 causes a problem in that the driving of the driving part 260 may be incomplete when the MEMS device is driven.
Further, in the stages of the fabrication process shown in FIGS. 2D and 2E, the connection part 261 of the MEMS structure layer, which is formed on an anchor part and the substrate 210, is formed in a bent shape that is relatively thinner than the anchor part and the MEMS structure layer.
Accordingly, the connection part 261 having a thin and bent shape causes a problem in the stability of the MEMS device, since the general operation of the MEMS device involves the movement of the MEMS structure, i.e., the driving part 260.
In an effort to solve the above problems, it is a feature of an embodiment of the present invention to provide a MEMS device having enhanced reliability and a stable driving capability and a fabrication method thereof.
The above feature of the present invention is provided by a first embodiment wherein a method for fabricating a MEMS device having a fixing part fixed to a substrate, a driving part connected to the fixing part by a connecting part, wherein the driving part is floating over the substrate, a driving electrode for driving the driving part by a predetermined driving force, and contact parts selectively switchable with the driving part, including patterning the driving electrode on the substrate; forming an insulation layer on the substrate on which the driving electrode is formed; patterning the insulation layer and etching a fixing region and a contact region of the insulation layer, in which the fixing part and the contact parts, respectively, are to be formed; forming a metal layer over the substrate including the fixing and contact regions; planarizing the metal layer until the insulation layer is exposed; forming a sacrificial layer on the substrate; patterning the sacrificial layer to form an opening exposing a portion of the insulation layer and the metal layer in the fixing region; forming a MEMS structure layer on the sacrificial layer to partially fill the opening, thereby forming sidewalls therein, wherein the MEMS structure layer forms the fixing part, the driving part and the connection part connecting the fixing part and the driving part on the sacrificial layer; and selectively removing a portion of the sacrificial layer by etching so that a portion of the sacrificial layer remains in the fixing region.
Preferably, the insulation layer is formed as a thick film having a thickness at least as thick as the thickness of the driving electrode so that the driving electrode is embedded in the insulation layer.
Preferably, in the step for forming the opening, the opening is substantially formed over the entire portion remaining except for the portion matched with a connection part connecting the fixing part and the driving part. A width of the connection part is preferably narrower than that of the fixing part.
Before the selective removal of the sacrificial layer, the method preferably further includes forming etching access holes in the MEMS structure layer. Preferably, the etching access holes are formed in the driving part of the MEMS structure layer.
Preferably, the insulation layer is a TetraEthyl OrthoSilicate (TEOS) oxide film. The metal layer is preferably gold. The planarization is preferably performed by polishing. The sacrificial layer is preferably a material selected from the group consisting of aluminum, copper, oxide, and nickel.
The above feature of the present invention may also be provided by a second embodiment wherein a method for fabricating a MEMS device having a fixing part fixed to a substrate, a driving part connected to the fixing part by a connecting part, wherein the driving part is floating over the substrate, a driving electrode for driving the driving part by a predetermined driving force, and contact parts selectively switchable with the driving part, including patterning the driving electrode on the substrate; forming a first insulation layer on the substrate on which the driving electrode is formed; patterning the insulation layer and etching a fixing region and a contact region of the insulation layer, in which the fixing part and the contact parts, respectively, are formed; forming a metal layer over the substrate including the fixing and contact regions; planarizing the metal layer until the driving electrode is exposed; forming a second insulation film covering the driving electrode to electrically isolate the driving electrode and the driving part; forming a sacrificial layer on the substrate; patterning the sacrificial layer to form an opening exposing a portion of the first insulation and the metal layer in the fixing region; forming a MEMS structure layer on the sacrificial layer to partially fill the opening, thereby forming sidewalls therein, wherein the MEMS structure layer forms the fixing part, the driving part, and the connection part connecting the fixing part and the driving part on the sacrificial layer; and selectively removing a portion of the sacrificial layer by etching so that a portion of the sacrificial layer remains in the fixing region.
The above feature of the present invention may also be provided by a MEMS device including a fixing part fixed to a substrate; a driving part connected to the fixing part by a connecting part and floating over the substrate; an electrode part for driving the driving part; and contact parts selectively switchable with the driving part, wherein the electrode part and the contact parts are planarized on the substrate.
Preferably, the electrode part includes an electrode and an insulation layer covering the electrode to electrically isolate the driving part and the electrode, the electrode being embedded in the insulation layer.
The MEMS device preferably also includes an anchor inserted between the fixing part and the substrate for fixing the fixing part on the substrate; and sidewalls on at least a portion of side surfaces of the anchor.
Preferably, the sidewalls are substantially formed over the entire portion remaining except for a portion corresponding to a connection part connecting the fixing part and the driving part. A width of the connection part is preferably narrower than that of the fixing part.
The sidewalls, fixing part, and driving part are preferably integrally formed in one body, and the sidewalls are in contact with the substrate.
Accordingly, the step difference between the RF lines and the driving electrode is removed, so the MEMS structure layer to be subsequently formed for the driving part driven by an electrostatic force can be prevented from being transformed.